Some scientists not involved in the studies say the research provides some of the first evidence on how trees react to carbon dioxide. Other scientists say the research disputes a belief among some coal and power companies. The companies say that rising levels of carbon dioxide in the atmosphere will not create harmful global warming. Instead, they say it will increase forests and other plants.

　　1.What is the purpose of this passage?

　　A) Introduce some new ideas about the relationship between trees and carbon dioxide.B) Introduce recent condition of global industrial pollution.

　　C) Call on people to plant more trees to reduce greenhouse gases.

　　D) Point out that power companies should be responsible for the rising levels of carbon dioxide.

　　2. Why researchers put trees in extra carbon dioxide in the first study?

　　A) To learn whether trees can still absorb carbon dioxide under extreme conditions.

　　B) To get more oxygen from these trees.

　　C) To evaluate the maximum carbon dioxide that trees can absorb.

　　D) To see the growth rate of these trees.

　　3.What happened to the leaves falling from the trees in the second study?

　　A)They broke down and the main parts turned into oxygen.

　　B)They broke down and the carbon content had mainly turned into carbon dioxide.

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